Democratic Sen. Tim Kaine leads Republican challenger Corey Stewart by 18 points in the U.S. Senate race in Virginia, according to a Quinnipiac University poll released Tuesday.

Mr. Kaine had a 54 percent to 36 percent lead over Mr. Stewart, including a 20-point advantage among independents, the poll showed.

“Virginia, which was once a solidly red state, has made the full transition to a blue bastion,” said Peter A. Brown, assistant director of the Quinnipiac Poll.

Republicans haven’t won a major statewide election in Virginia since 2009.

About 56 percent of voters said they approve of how Mr. Kaine is handling his job as U.S. senator — the same percentage who said they disapprove of how President Trump is handling his job.

“The office-holder they don’t like is President Donald Trump, whose job approval is strongly negative. Voters see candidates who embrace him negatively,” Mr. Brown said.

Voters are still getting to know Mr. Stewart, who ran on an unabashedly pro-Trump message ahead of his win in a GOP primary contest two weeks ago.

Four in 10 said they don’t know enough about Mr. Stewart to form an opinion of him, with the rest about evenly split between having a favorable and an unfavorable view.

Mr. Stewart, who has also made preserving the state’s Confederate and historical monuments a key part of his message this year and in last year’s governor’s race, did get some good news in the poll on that front.

Fifty-seven percent of Virginia voters said they oppose removing Confederate monuments from government property in the state, compared to 33 percent who said they support removing them.

A narrow plurality of voters also said they think the Confederate flag is more a symbol of southern pride, as opposed to more a symbol of racism.

The survey of 1,082 Virginia voters was conducted from June 21-25 and has a margin of error of plus or minus 3.7 percentage points.